Biomedical subjects

R Manninen

Publications and source records attributed to R Manninen.

4 recordsLinked to original sources

PubMed1998

Reliability of disc diffusion susceptibility testing of Streptococcus pneumoniae and adjustment of laboratory-specific breakpoints. Finnish Study Group for Antimicrobial Resistance.

A routine disc diffusion method for detecting antibiotic-resistant Streptococcus pneumoniae was evaluated in 20 clinical microbiology laboratories. Fifty consecutive clinical isolates were tested by disc diffusion in each laboratory, and collected for MIC determinations. Participating laboratories used three disc types and several media; altogether 17 disc-medium-breakpoint reference combinations were used. Of the 781 isolates, 1.2% were resistant to penicillin and 4.2% were intermediately resistant. Eight of the nine resistant isolates had been classified as resistant to penicillin using a 1 microgram oxacillin disc screening test in the participating laboratories. If the MIC was taken as 0.125 mg/L, which is just above the intermediate breakpoint, 11 of 12 isolates were interpreted as susceptible to penicillin with the oxacillin disc test. The laboratories using Oxoid or Biodisk paper discs performed better in detecting co-trimoxazole resistance than the laboratories using Rosco tablets. Two control strains (one multiresistant and one susceptible) were each tested in the laboratories ten times. Based on these results laboratory-specific breakpoints for tetracycline were determined linearly. These adjusted breakpoints corrected three of five false-susceptible interpretations of the resistant clinical isolates and reduced the number of minor errors from 8.5% to 2.6%.

Anti-Bacterial Agents↗

PubMed1998

Clinical microbiology laboratories do not always detect resistance of Haemophilus influenzae with disk or tablet diffusion methods. Finnish Study Group for Antimicrobial Resistance (FiRe).

The performance of disk diffusion testing of Haemophilus influenzae was evaluated in 20 laboratories. Thirteen disk-medium-breakpoint-inoculum modifications were used in Finnish clinical microbiology laboratories. The performance of various methods was evaluated by testing a susceptible control strain and one with non-beta-lactamase-mediated ampicillin resistance 10 times in 16 laboratories. Gaps in millimeters were measured between these two groups of results. The strains were separated by a gap of at least 5 mm in 8/16 laboratories testing ampicillin, in 7/15 laboratories testing cefaclor, in 5/ 16 laboratories testing cefuroxime, and in 15/16 laboratories testing trimethoprim-sulfa. Detection of ampicillin resistance was better with 2.5 microg tablets than with 10 microg disks or 33 microg tablets. For MIC-determinations, 785 isolates and their disk diffusion results were collected. None of the 12 clinical isolates with non-beta-lactamase-mediated ampicillin resistance was detected as resistant in the participating laboratories. The ampicillin and cefaclor results of the isolates were no better even when a laboratory was able to separate the control strains. Cefaclor results were unreliable because of poor disk diffusion-MIC correspondence and incoherent breakpoint references. Interlaboratory variation of the zone diameters caused false intermediate results of cefuroxime-susceptible strains. When ampicillin, cefaclor and cefuroxime were tested, the discrimination of laboratories using disks and tablets was equal, whereas the laboratories using paper disks were better able to detect trimethoprim-sulfa resistance.

Diffusion↗

PubMed1997

Increasing antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis in Finland.

Respiratory and otitis isolates of 807 Streptococcus pneumoniae, 816 Haemophilus influenzae and 446 Moraxella catarrhalis were collected from 21 clinical microbiology laboratories for antimicrobial susceptibility testing in 1995. After a period of relative stability in 1981 and 1987-1990, beta-lactamase production increased in H. influenzae. Among middle ear isolates from children under 6 years, beta-lactamase production increased from 8% to 24% in H. influenzae and from 81% to 96% in M. catarrhalis since the survey in 1987-1990. 1.2% of S. pneumoniae were penicillin-resistant and 4.2% intermediately resistant; 5 years earlier among otitis isolates of children only 1.7% intermediate resistance was found. Ampicillin resistance was seen among 1.9% of non-beta-lactamase-producing strains of H. influenzae. Resistance to trimethoprim-sulphamethoxazole occurred in 9.4% of S. pneumoniae, 7.4% of H. influenzae and 0.7% of M. catarrhalis. Frequencies of azithromycin resistance were 3.0% in S. pneumoniae and 1.6% in H. influenzae, and those of tetracycline resistance were 6.7% in S. pneumoniae and 1.2% in H. influenzae.

Adolescent↗

PubMed1995

Disk diffusion susceptibility tests: need for laboratory-specific breakpoints.

Significant changes were observed in the measured resistance levels of Escherichia coli and Staphylococcus aureus when the Biodisk disk susceptibility test method used in 1992 was replaced with another commercial method, Oxoid. For example, when non-species-specific breakpoints were used, the frequency of cephalotin-resistant E. coli was 12% of all isolates in 1992 but only 4% in 1993; the corresponding figures for the intermediately resistant isolates were 84% and 8%. The population distribution histograms were however, practically unchanged. Thus, the resistance percentages apparently did not reflect the real development of resistance. Similar findings were also made for several other antimicrobials. Susceptibility test breakpoints should therefore be examined separately for all bacterial species in each laboratory, and the application of adjusted laboratory-specific breakpoints should be considered. For this purpose, the WHONET computer program provides excellent assistance.

Ampicillin↗